Cytoplasmic polyadenylation is an evolutionarily
conserved mechanism regulating translational activation
of a set of quiescent maternal messenger RNAs (mRNAs)
during early development. Cytoplasmic poly(A) elongation
occurs in a wide range of species, ranging from clam to
mouse. The relevance of this process during late oogenesis
and early embryogenesis has been shown by studies in the
mouse, Xenopus, and Drosophila.
In mouse and Xenopus, the only vertebrates so far examined,
the critical regulatory sequences, referred to as
Cytoplasmic Polyadenylation Elements (CPEs), are AU-rich
and located in the 3' untranslated region (3'-UTR) near the
canonical nuclear polyadenylation element (AAUAAA), which
also is required for proper poly(A) addition.
The CPE has the general structure of UUUUUUAU.
However, the CPE is not identical in all mRNAs and its
position varies relative to AAUAAA (generally within 100
nucleotides). The minimal CPE capable to stimulate
elongation of a poly(A) tail appears to be UUUUAU, and
recent experiments show also the existence of substantial
context and position effects on CPE function.